This invention relates generally to liquid flow distributors, and in particular to a distributor for an expanded or fluidized bed reactor, the distributor permitting unimpeded forward flow of liquids carrying stringy solids and also functioning to prevent backflow of the fluidized media when forward flow through the reactor is arrested.
In a fluidized bed reactor for treating industrial or municipal wastewater, the wastewater is conducted upwardly through a bed of seeded carrier particles such as sand. In the course of operation, these particles are enlarged by the biological growth of cellular material. Because the particles in the bed are suspended by the upwardly flowing liquid stream and are in continuous motion, an enormous surface area is available for such biological growth. Fluidized bed reactors of this type are disclosed in U.S. Pat. Nos. 3,846,289; 3,956,129; 4,009,098 and 4,009,099.
In a fluidized reactor, the incoming wastewater must be dispersed throughout the bed, and for this purpose use is made of a network of outlets forming a flow distributor. Thus U.S. Pat. No. 4,202,774 to Kos discloses a flow distributor having an array of ports so arranged as to assure a smooth, low turbulent flow of liquid into the reactor to effectively fluidize the bed particles therein.
Wastewater to be treated often carries stringy solids which, when passing through a conduit having an obstruction therein, tend to collect about the obstruction and thereby clog the passage. The primary concern of the present invention is with a liquid flow distributor that will allow stringy solids carried by the wastewater being treated to pass through the distributor without causing clogging, the distributor preventing the media being fluidized from flowing therein as a result of backflow when forward flow is arrested. Inasmuch as in a conventional fluidized bed reactor, a head of clear effluent is developed above the fluidized bed, should forward flow through the reactor be stopped, the effluent may then backflow through the bed and in the course thereof seek to transport toward the distributor, particles derived from the bed.
In general, devices heretofore employed to distribute a liquid or gas into a fluidized bed fall into two distinct classes. One type, such as that disclosed in the Olavson U.S. Pat. No. 3,334,819 makes use of conical nozzles which act to resist backflow of the fluidized media into the distributor when the process is brought to a halt. But such nozzles are subject to clogging should the wastewater or other fluidized medium have stringy solids therein.
The second type, such as that disclosed in Perry's Chemical Engineer's Handbook, makes use of a T-bar distributor usable in those situations in which the liquid or gas fluidizing medium contains stringy solids. However, this distributor has the disadvantage of permitting flowback of the fluidized media into the distribution ports when the process is arrested.
Commercially-available underdrain nozzles for filters, such as those described in U.S. Pat. No. 3,472,382, are similar to those used in fluidized bed reactors, use being made of a strainer to prevent media backflow. But such strainers interfere with forward flow when the fluid being filtered carries stringy solids. While the present invention will be described in the context of fluidized bed reactors, it is to be understood that the distributors disclosed herein are also useful as an underdrain for a filter.